Since Dupont (USA) invented aromatic polyimide compounds in 1955, various polyimide films and products with different structures and properties have been developed. Owning to advantages such as good mechanical properties, electrical properties, and resistance to radiation and heat, polyimides have found broad applications in the fields of aerospace, electronics, automobile, and telecommunication, etc. Nevertheless, the molecular structure of polyimides makes them poorly meltable and poorly dissolvable, which causes great inconvenience for their practical applications. Thus modification of polyimides becomes hot spots, intensively studied by scientists worldwide. In fact, scientists have made great achievements. For example, Dupont (USA) developed Kapton films in 1962, which are synthesized through a condensation reaction between a pyromellitic dianhydride and a triphenyl diether diamine, have heat resistance close to the limit, and have good performance to price ratio. The Kapton films are still the dominant product among various heat-resistant resins until now, and have wide applications in the fields of military, aerospace, electronics, electrical appliance, and automobile. In the 1980s, Ube Industries (Japan) synthesized high performance full-aromatic polyimides from 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline. Products prepared from these polyimides, such as polyimide films Upilex-R and Upilex-S, especially Upilex-S, have higher rigidity and mechanical strength, low shrinkage ratio, low thermal expansion coefficient, and much lower water permeability and gas permeability. More significantly, their hydrolysis stability is much higher than Kapton films. Therefore, they exhibit tremendous value in the microelectronic field, and become the most noticeably competitive products. Other examples include Apical PI films developed by Kaneka corporation (Japan), Ultem polyether imide (PEI) plastic developed by GE(USA), and Torlon poly(amide imide) (PAI) developed by Amoco.
Until now, polyimide compounds with various performance characteristics are available in the polyimide market. However, as technology is being developed toward higher end and refined applications, more challenging, demanding, and comprehensive performance requirements have to be met by polyimides used in the field of aerospace, microelectronics, electronics, electrical appliance, and automobile, such as higher peel strength and tear strength, good flexibility, and high glass transition temperature. Until now reports related to that type of polyimides are rare in both the Chinese domestic and international markets.
CN 1529546A discloses a preparation method of cover films used in flexible printed circuit board. The method comprises preparing a 25% chloroform solution from EX-48 brominated epoxy resin (20-30 parts), E-12 bisphenol-A epoxy resin (16-20 parts), F-44 phenolic epoxy resin (8-12 parts), Hytrel thermoplastic elastomer (14-29 parts), a thermoplastic carboxylated acrylonitrile-butadiene rubber (8-14 parts), an arylamine curing agent (diamino diphenyl methane) (4 parts), and a modified dicyanodiamide (8 parts). The method further comprises coating the 25% chloroform solution onto a polyimide film, drying the polyimide film at 80-90° C. for 15 minutes to form a 15-20 microns coat, and isolating the coat by using polyester or release paper to produce the cover film.
CN 1123589C discloses a thermosetting polyimide base resin, which is prepared from an aromatic tetracarboxylic dianhydride (100 weight parts), an aromatic diamine (35-110 weight parts), and a reactive aliphatic dicarboxylic acid (10-55 weight parts). The reactive aliphatic dicarboxylic acid is an organic compound with the following chemical structure:
wherein R is H, methyl, or ethyl. The resin can be used at 310-320° C. for a long period of time. Compared with PMR-15, the cured material has excellent anti-shock performance characteristics. The carbon fiber-reinforced resin-based composite material prepared from the same has significantly reduced microcracking in high temperature applications.
CN 1693338A discloses a multi-block copolymerized polyimide, with the following chemical structure:
Its preparation method comprises (1) dissolving an aromatic diamine in N,N-dimethyl acetylamide (DMAc); (2) adding an aromatic dianhydride at a certain ratio while stirring to allow the aromatic diamine and the aromatic dianhydride to react at 0-25° C. for 4-6 hours to produce an amino- or anhydride-terminated oligomer solution; (3) further sequentially adding other dianhydride(s) and diamine(s) to allow the same to fully react for 6-8 hours to provide a copolymer with a block structure; (4) preparing the copolymerized polyimide powder or film from the copolymer by chemical imidization or thermal imidization; wherein the aromatic dianhydride is 3,3′,4,4′-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride; the aromatic diamine is one or more of 4,4′-oxydianiline and bisphenol-A diamine; the other dianhydride can be one or more of 4,4′-carbonyldiphthalic anhydride, 4,4′-oxydiphthalic anhydride, bisphenol A dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride; the other diamine can be one or more of benzophenone diamine, phenylene diamine, 1,3-bis(4-aminophenoxy)benzene (1,3,4-APB), 1,4-bis(4-aminophenoxy)benzene(1,4,4-APB), and 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane. The multi-block copolymerized polyimide has good heat resistance and mechanical properties, whose rigidity and processability can be adjusted by regulating the composition of the multi-block copolymerized polyimide.
Although the aforementioned polyimide materials are good in certain performance, they do not simultaneously have good peel strength, tear strength, and flexibility, and high glass transition temperature. As technology is being developed toward higher end and refined applications, more challenging, demanding, and comprehensive performance requirements have to be met by polyimides used in the field of aerospace, microelectronics, electronics, electrical appliance, and automobile. Polyimide materials are required to have high peel strength and tear strength, good flexibility, and high glass transition temperature simultaneously.